The invention relates to a composite fabric for use as clothing for the sheet forming section of a papermaking machine. In particular it relates to a composite fabric of the aforementioned type having at least two fabric layers formed by transversely and by longitudinally extending threads and interconnected by transversely or by longitudinally extending threads.
Clothings for the sheet forming section of a papermaking machine, so-called papermachine screens, have to meet rigid requirements. The paper supporting side of a papermachine screen has to be be designed so that it leaves minimal marks in the paper. Owing to the increase in costs for raw materials and the growing use of waste paper having a high content of short fibers, good retention is also important. The underside, or running side, of the papermachine screen is subject to high wear on account of the high operating speeds and the use of less expensive filler material that is more prone to abrasion. This high wear tends to decrease the service life of the papermachine screen. The power input of the screen section is furthermore limited, in part by the exhaustion of the installed power and, in part by the high cost of energy.
Attempts to meet these partially conflicting requirements for papermachine screens have resulted in the development of screens containing a plurality of fabric layers loosely interconnected by additional binder threads. German Offenlegungsschriften Nos. 2,455,184 and 2,455,185 describe circularly woven papermachine screens of this type wherein interconnection of the fiber layers is made with a binder warp, i.e. in the final papermachine screen the binder threads extend in the cross-machine direction. A similar papermachine screen has been known from German Offenlegungsschrift No. 2,917,694 which, however, is woven flat and contains binder weft wires also in the cross-machine direction.
Papermachine screens made in accordance with these prior art techniques, i.e., with binder wires in the cross-machine direction, are not always satisfactory. In particular, when used in kraft, paperboard or cardboard machines they do not exhibit a sufficiently long service life.
It is therefore a primary object of the present invention to provide a composite fabric of the previously mentioned type having a long service life when used in kraft, paperboard and cardboard machines as well as other types of papermachines.